Binary Large Objects (BLOBs)¶

BLOBs are very large, variable length, binary or character data objects. BLOBS are typically used to store documents, pictures, or other variably structured (or unstructured) items.

When a DataFlex text field is too large for the native type, the Mertech drivers automatically use the BLOB data type during the migration. For example in MS SQL Server the driver automatically switches from varchar (<string length>) to varchar (max) when database limitations are hit.

As long as the size of the object fits in a regular DataFlex string, the object is bound as any regular TEXT column. The Mertech drivers transparently handle this, defaulting to non-BLOB data types if possible.

BLOBs can either be stored inside the database or in the file system. Storing BLOB data in the database offers a number of advantages:

• Security measures used to control access to the database can also be used to control access to BLOBs.

• Backup routines used to backup the database can be used to capture BLOB data as well, simplifying maintenance.

• Transaction control, if required, is built into the database.

• Search operations can be performed against formatted text-based data contained within BLOB fields—for example, Microsoft Word or Microsoft Excel documents.

The file system may be a better storage choice for BLOBs when:

• The object requires significant overhead to process, e.g., streaming video.

• The cost of storage space is a consideration.

• The object will be modified frequently. The file system may handle fragmentation better than the database server.

For all databases, there is a slight performance penalty fetching BLOB data, because BLOB data is not stored in the same internal page as the rest of the record.